Moralists had, as a rule, regarded it as a mode of warning, had claimed for it a certain ethical efficacy in the formation of character, had praised it as something that taught us what to follow and showed us what to avoid.

There are no more uses of "efficacy" in the book.

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The doctor weighed the efficacy of each treatment against potential side-effects.

They held hearings to investigate concerns about the safety and efficacy of the vaccine.